Function generator



March 30, 1965 c. B. VAUGHAN 3, 7 7

FUNCTION GENERATOR Filed April 19. 1962 2 Sheets-Sheet 1 422A 55a 43a f m T 403 444 2 428 450 434 452 400 435 l 452 404 402 68 66 FIG. 1

INVENTOR.

CARROLL B. l/AuaHA/v BY FIG.. 3

AITOI/VEY United States Patent Ofiice 3 ,176 ,157 Patented Mare 30, 1965 3,176,157 FUNCTION GENERATOR Carroll B. Vaughan, East Orange, NJ., assignor to The Bendix Corporation, Teterboro, NJ., a corporation of The invention relates to function generators and more particularly to function generators of the capacitive discharge type.

An object of the invention is to provide a novel function generator.

Another object of the invention is to provide a novel function generator having extremely fast rise time and good fall time.

Another object of the invention is to provide a novel function generator having a low (theoretical zero) source impedance.

Another object of the invention is to provide a novel function generator capable of driving into a purely reactive load.

Another object of the invention is to provide a novel function generator capable of producinga signal attenuable from either the positive to negative direction or the negative to positive direction.

Another object of the invention is to provide a novel function generator having fast rise time, good fall time, low source impedance, the ability to feed into capacitive load, both positive and negative attenuable output and having two outputs at 180 phase shifted from the other.

Another object of the invention is to provide a novel function generator having an improved power transfer ratio.

The invention is a novel function generator that provides a plurality of selectable wave forms including, for example, a pulse, a step, square waves, and a train of spikes at low frequency and high frequency or of adjustable frequency and of adjustable duty cycle. Each one of these wave forms is attenuable, capable of polarity reversal, and is floating. By floating, it is meant that the generated function is adjustably referenced to a common point. By attenuable, it is meant that the signal level of the generated function can be reduced from the positive to negative direct-ions and vice versa, or explained in terms of binary logic, the logic one signal level voltage can be reduced from logic one level to the logic zero level and vice versa. It is also desirable that the wave forms of the function generator have a fast rise time and a good fall time with capacitive and inductive loads.

Summarized below are eleven features of the novel function generator which is 'shown in two alternative embodiments in FIGURES 1 through 5.

(1) A theoretical zero source impedance, 7 (2) Ability to drive into a capacitive load, (3) Very fast rise time,

(4) Very good fall time,

. (11) A square wave output capability..

These and other objects and features of the invention are pointed out in the following description in terms of the embodiments thereof which are shown in the accompanying drawings. It is to be understood, however, that (5) Attenuation from maximum to minimum of a pdsithe drawings are for the purpose of illustration only and are not a definition of the limits of the invention, ref erence being had to the appended claims for this purpose.

In the drawings:

FIGURE 1 is a schematic drawing showing a basic novel function generator.

FIGURE 2 is a detailed wiring diagram of the novel function generator of FIGURE 1.

FIGURE 3 is a wiring diagram of the novel function generator of FIGURE 2 and showing parasitic capacitance in the circuit.

FIGURE 4 is a wiring diagram of a modified form of the novel function generator.

FIGURE 5 is a wiring diagram of another modified form of the novel function generator showing the function generator with two outputs.

The basic operation of the novel function generator is described in conjunction with the schematic drawing of FIGURE 1 wherein there is shown an adjustable DC. power supply 401, a two terminal load 400; a single pole double throw switch 402; and two large capacitors 403 and 404.

The floating power supply 401 may be of a conventional type such as a multiple tapped battery or a series connected dry or storage cell, or of a type such as shown in FIGURE 2 and described and claimed in U.S. applica tion Serial No. 166,224, filed by Carroll B. Vaughan and assigned to The Bendix Corporation. The power supply 401 provides three separately adjustable D.C. voltages respectively at output terminals 422, 424, and 426. The voltages at terminals 422, 424, and 426 are floating with respect to ground, according to a voltage applied at a common terminal 428. The voltage available at the first terminal 422, also called the high positive terminal, is always positive with respect to common 428. The voltage available at the second voltage output terminal 424 called the positive or one terminal is always positive with respect to common 428, and is always smaller in magnitude than the voltage available at the high positive terminal 422. The voltage available at the third terminal 426, also called the negative or zero terminal, is always negative with respect to common 428.

The load 400 is of a two terminal type, with a positive side 430 connected by a conductor 432 to the high positive terminal 422. A negative side 434 of the load 400 is connected by a conductor 436 to a switch 402. The switch 402 in the FIGURE 1 is shown as a single pole double throw type switch, having a switch blade terminal 441 connected to the conductor 436, a switch blade 442, and two contacts 444 and 446.

The two capacitors 403 and 404 as shown in FIGURE 1 are serially connected together at a juncture 450 which is connected by a conductor 452 to the common terminal 428. The other plate 433 of capacitor 403 is connected by conductors 454 and 456 to one contact 444 of the switch 402. The plate 433 is also connected by conductors 454 and 458 to the positive output terminal 424 of the power supply 401. Thus, an instantaneous positive D.C. potential is always available at contact 444. This potential is stored across the plates of capacitors 403 and is equal in magnitude to the potential drop between the voltage available at the positive output terminal 424 and the common potential terminal 428.

Likewise, capacitor 404, as shown in FIGURE 1, is connected with its positive side, or positive plates 460, to common by the conductor 452; and its negative plate 462 is connected by conductor 464 and 466 to the second contact 446 of the switch 402. The negative plate 462 of capacitor 404 is also connected by conductor 464 and 468 to the negative adjustable source of DC. voltage, available at the negative terminal 426. Thus, a negative potential (relative to common) of theoretical zero resistive I I 7: rs o impedance is always available at terminal 446 of switch 402;

By operating theswitch blade 442 of the switch 492 in one position (e.g. 44-4) or in the other position (cg. 446), the voltage across the load is abruptly changed. A feature of the novel function generator is that the negative side 434 of the load 48%) is always fed by a source of D.C. voltage with substantially zero resistive source imtion applied to and as'seen by the load 4 is very fast,

regardless of the capacitance of the load 42%. i

The positive side 439 of the load 400 is held at a fixed potential equalto the potential. available at'the high positive terminal 422 while the negative side 434 of the load 404) receives a'discontinuous potential according to the operation ofswitch'402; Thetwo potentials available at contacts 444- and'446 of the switch 4&2 correspond to.

the logic one andthe logic zero levels commonly required in computer operation. The zero and one levels are selected byadjusting the voltages available at the voltage output terminals 422, 424, and 426, and at the common potential terminal 428; furthermore, the voltage function is 'attenuable from either the zero or one level by adjusting the voltage at the one and zero terminals 424 and 426. These features are now pointed up by way of example.

Assume, for example, that the voltage available at ter :minal 422 is adjusted to +16 volts relative to common and voltage availableat terminal 424 is +12 volts relative to common-428; and the voltage available at the zero terminal 426 is 12 volts relative to common 428, and the common voltage atterminal 428 is .l6 volts relative to' ground. "Thus, the logic onef level at terminal 424 is equal to +12 volts relative to common and -'4 volts rel- I ative to ground and the logic zero level at terminal 426 '-is equal to -12volts"relative tocommon and 28.volts relative to ground. It is'seen that the size oithe signal between the logic zero andthe logic one level is determined by' the dilferencein voltage available at terminal 4-2.4 and426; while therelative value of the logic zero and logic one withiespectito ground are determined by thepotential applied between the common terminal 428 and ground.' The'signal applied to the load 4% can be attenuated either in the positive going or negative going sense by adjusting the voltage available at the one or zero terminals 42tor 426. Thus,,the voltage, across. load'40fi is the sum of voltage from 422 tocommon plus 'pedance, thus the rise and fall timefof the voltage. functern in which the function generator and load is a part.

The size of the load capacitor 412should be small in com f parison with the size of thecapacijtors 403 and 434'.

positive or one terminal'424;

The switching action performed by the switch 492 of FIGURE I can beperformed manually'as shown therein or may be performed automatically by two transistors as 7 shown in FIGURE 2. Referring to FIGURE 2 there is shown therein a basic function generator of FIGURE 2 (with the detailed power supply 4G1 as described above) and with a transistor switching circuit 5tl2.1 V

The switching circuit 5ti2 comprises two transistors, an NPN transistor 595 and a PNP transistor 5% each havinga base5ll0 and 511 respectively, andernitter 512 and i 513 respectively, and acollector 514 and 515 respectively.

The bases 510 and 511 of the transistors 5'35 and 56. are tied 'together'by a conductor 518; and the emitters 512 and 513are tied together by a conductor 519; The emitters 512 and 513 are connected through conductors 519 and 9836 to the negative sided-34 of the load 4titl. The collector 514 of the NPN transistor 5:95 is connected by conductor 444 through a diode 530 and a conductor 456 to the positive side 433 of capacitor. 4%, and'to the high The vcollector Slii of the PNP'transistor 506 is connectedby conductor 446, 466, and 464 torthe negative 7 side 462 of the capacitor 404; and isalso connected by 35 conductors 4.64; and 468 to the negative, 'orfzero 'terminal426. l l r Each transistor 505 or 50 6openateslas a one way single pole switch with one switch open while the other is closed and vice versa;

The transistors 505 and 506. aremade to altematively conduct and be cut off by a driver circuit 509 of conventional type, connected between the bases 510 and 511,

j and emitters 512 and 513 of the-transistors 505kaind 506 by conductors 516 and 518, 517 and 519. The driver cirvoltage amt-26 for switch 402 of FIGURE 1 in the down position 446; and diiference of voltage between 422 and 424 for switch 402 in the up position.

. FIGURE 2-is a detailed wiring diagram of the novel function generator'of FIGURE 1, and like'elements in the FIGURES I ancl2 bear like legends. The power supply 401 of FIGURE 1 may be of any conventional or convenient typejhavingthree separate adjustableDC. output voltages relative to a common potential, and maybe'a cuit 5%9 is a conventional multifunction generator, operator operative, for producing .a plurality of wave forms, eg. 'step, pulse, square Waves, and pulse trains of variable frequency and duty cycle. The-application of a positive signal to the bases 510 land 511 relative to emitters 512 and "513 by driver circuit 509 through conductors 516 and 513 respectively, will cause the NPN transistor 595 to conduct and the other PNP transistor'506 not to conduct.

multi-independentbrush auto transformer of the kind described inVaughan, US. application Serial No. 166,-

224, filed January 15,1962, andas shown in FIGURE 2. 1 The power supply 401 of FIGURE 2 includes a source of electrical'potential 470 which may, for example, be

I 117 volts A.C. commonly available applied to an isola:

tion transformer 471 and then in to the winding of'the inulti-indepehdent brush auto'transformer 472 having at least three adjustable outputs 475,476, and 477. The voltages at each output 475, 476, and 477 are applied respectively to. the'diode rectifiers 481, 482, and 483; and

filter capacitors 484, 463,, and 404. It is to benoted that when the function generatorfincludes the power supply 'havinga multi-independent brush autoxtransformer as shown in FIGURE 2 the filter capacitors of the power supply performs a dual function inlthat they rectify and act as charging capacitor for the function generator. In

' particularsthe capacitor 403 is both the filter capacitor of I the rectifyingcircuit of output terminal 476, and at the samet'ime, is the charging capacitor for the function gen- V The application of an electrical signal from the driver circuit 509 through conductors 516jand 518 to the bases 510 and 511 of a negativepolarity, relative to the elec trical signal applied to the emitters 512 and 513, will cause the other transistor PNP .506 to conduct and/the first transistor NPN-5tl5n1ot to' conduct. Thus, the frequency, and the duty cycle, :as well was D.C. operation,

of the driver circuit 509is taithfullyrep-roduced by the function. generator. The PNP transistor 506 is used in charging circuitscorresponding to the switch blade 442 "of switch 402 being in'the downl position-in contact 'j'w ith contact 446. The NPN transistor 505 is used in the discharge circuit cor-responding 110 the switch blade 44-2 of switch 402 in the up position making contact to contact 444.

The chief disadvantage 0f the arrangement shown is ftlrat driver 509 is isolated and floating in that it is not ing power "supply.

grounded or other-wise connected to common potential, and in particular, its power must be supplied by a float- Three diodes 530,732, and 534 are; included in the circuit. Their functions are explained each in turn.

The diode bearing legend S'Stllisa blocking diode and is pacitcr 412.

connected from the collector 514 of the transistor 505 to the positive plate 433 of capacitor 403. Its function is to prevent the NPN transistor 505 from receiving a reverse voltage.

The clamping recharge diode 532 is connected in the negative side 434 of load 400 to the positive plate 433 of the capacitor 403. It functions as a clamp to prevent the capacitor 412 of the load 400 from discharging through the resistor 411 of the load 400 when the NPN transistor 505 is in a conducting state, and thus prevents the load trom discharging beyond the logic one level. A protecting diode 534 is mounted back biased across the load with anode to the negative side 434 and cathode -to positive side 430 of the load, to prevent reverse surge currents across the transistors 505 and 506. With the load shown, there will be no reverse inductive surge current upon the switching of the transistors 505 and 506.

. circuit) should be smaller than the charging capacitors 403 and 404 to alternately permit the charging capacitor to discharge into the load capacitor 412, and the load capacitor 412 to discharge to the difference voltage be tween 484 and 403. Thus the charging capacitor should always be at least ten times greater than the load ca- In practice, the charging capacitors 403 and 404 may,

for example, be on the order of 1000 microfarads. The

presently commercially available capacitors of this size have leakage resistances and inductances which interfere with quick charging and discharging; thus a small capacitor 503 and 504 is added inparallel with each larger capacitor 403 and 404; such small capacitors being of very high quality to provide upon switching the initia rise or fall of charge to or from the load. i In practical construction of this circuit, there are parasitic and distributed capacitances throughout the cirand the positivepower supply terminal 424, .a capacitance 522 between the negative side 434 of the load 400 and the high positive power supply terminal .422, a capacitance 523 between the negative side 434 of the load 400 and the common terminal 428, a capacitance 524 between the negative side of the load and the negative power supply terminal 426. All of these capacitances are small and are effectively charged or discharged every time switch 502 operates. They do not effect the operation of the function generator in any manner. There are also other parasitic and distributed capacitances in the circuit but these capacitances do not adversely effect the operation of the novel function generator.

An alternative embodiment of the novel function genload 400. The emitter 552 is connected to the negative plate 462 of the charging capacitor 404.

The base 551 is connected to an output of a driver circuit 544. The driver circuit applies to the base 551, :signals to make the transistor 542 conduct or nonconduct. When the transistor 542 is conducting, the negative side 434 of the load 400.is directly connected to the negative term-inal426 and to the plate 462 of capacitor 404, so that the logic zero potential at plate 462 of the capacitor 404 and terminal 426 is impressed on the load, and there is an electron flow from the charge stored on capacitor 404 through transistor 542, (from the emitter 552 to the collector 553) and into the load 400 charging the capacitance 412 of the load 400. Thus, when the transistor goes from nonconducting to conducting, the load receives a voltage change with almost zero rise time, because the source impedance seen by the load is purely reactive.

When the transistor 542 switches from a conducting to a non'conducting state, the charged capacitors 412 of the load cannot discharge through the transistor 542 or through the diode 540. In particular, the load capacitor 412 is charged to the high positive potential (for examample, 12 volts). The only path for the capacitor 412 to discharge is through the load resistance 411. For high resistance in 411, the time constant of the discharge is slow and produces a poor fall time.

To speed up the fall time, a speed up shunt load resistor 546 is added in 'parallel with the load. This is a resistor having a resistance such that the time constant of the load capacitance 412- times the parallel combination of the speed up shunt load resistor 546 with the load resistor 411 is small. Once the capacitor 412 of the load has discharged through the parallel combination of the speed up shunt load resistor 546 and the load resistor 41 1 to a potential, (in this example, equal to the logic one level, i.e. to j-[- 12 volts), the diode 540 becomes conducting and clamps the negative side 434 of the load 400 to the one potential level, (in the example, +12 volts). An advantage of the alternative embodiment of FIGURE 4 is that driver 544 has acommon connection and therefore is not floating as is the driver 509, in the circuit of FIGURE 2.

FIGURE 5 shows the circuitry by which the function generator supplies a second output inverted or 180 phase shifted from the first output. The function generator of the FIGURE 5 is similar to the generator of the preceding figures, and common elements bear the same erato-r is shown in FIGURE 4 wherein the power supply 401, the two charging capacitors 403 and 404, and the load I 400 are all interconnected as before and bear the same legends as in the preceding three figures. The switching action is performed by the combination of a diode 540, a transistor 542 and a driver circuit 544. The diode 540 is connected forward biased from the negative side 434 of the load 400 to the positive plate 433 of capacitor 403. Thus when transistor 542 is nonconducting, the negative side 434 of the load is directly connected to the potential of the logic one terminal 424 of the power supply 401.

Transistor 542 is a NPN transistor having a base 551,

-emitter*552, and collector 553. The collector 553 is conlegend. In FIGURE 5, there is a second pair of contacts 558 and 559 for a second load 400 There is also a second diode 560 and a second speed up shunt load resistor 563 and an additional NPN transistor 562 having an inverter 564 between the output of the repeater circuit 544 and input to the additional transistor 562. The output wave form from the driver circuit 544 is fed to an inverter 564 which inverts the signal of the driver 544 and applies it to the base 565 of the transistor 562.

The transistor 542 is turned on by the repeater circuit when the transistor 562 is turned off by the inverted signal from the inverter 564; and likewise transistor 542 is turned oil when the transistor 562 is turned on. Thereby the part of the circuit to the right of the dotted line AA operates phase shifted from the part of the circuit to the left of the dotted line; and a load connected at terminals 558 and 559 sees a wave form 180 phase shifted with respect to a load connected between terminals 430 and 434. V

. The circuit of FIGURE 5 may be modified and simplified by replacing the inverter 564 and the transistor 562 by a singlePNP transistor (not shown) with its V acrossll oad 40 are definition of thelimitscof the invention. p t v, f -Whatis claimed'ist'j i collector at reminisce and its emitter at terminarsse,

and its basei receiving theoutputtof driver'54-4, directly. w The PNP transistor'that replaces the inverter 564 and r NPN'transistor562must have matched compatible characteristics with NPN transistor'542. .With this arrange- "ment, the signal across load dtitland the inverted signal symmetrically identical and, 18Q

out of phase; 1

While several embodiments crime invention have been illustratedt'and described;various-changes 'in theform and relativei'arrangements of the'parts which will 'now 7 appear to those skilled in the art may be made without departing from the scope of the invention; a Reference is; thereforegto'behadtb the appended claims for a [1 l. .A :function generator comprising capacitive; means having a plurality of. terminals; a source of electrical means-to electrically connect the; other. terminal or the sources of electrical potential and to the juncture of the two capacitors, a two terminalelectrical loadlhaving one terminal of'the load attached to the third source ofdifferent'electrical potentiah and a switchingmeans for selectively connecting the other terminal of the load alternatively to oneend of the series corinectedwcapacitors and to the other end of the series connected capacitors; -sa'id'switching means including'a NPNand aPNP transistor' each havinga base, an emitter, and a Collector and with the bases joined together and-with the emitters joined together, "said emitters connected to the other tervminal of the load'and withthe collector of the NPN connected Eto the second sou rceiof electrical potential and with the collector of the PNP transistor con- 'nected to; the first source of? electrical potential, a driver circuit :connected .between the basesand emitters of said two transistors for selectively simultaneously making onetransistor conduct andthe 'other'non'conductive,

a diode connected between the other terminal of the lo ad 'and the' second source of electrical potential forumaintaining the loadzinf. a"fixedelectrical potential when the NPN transistor is conducting, a. second diode connected from the collector of the NPN transistor to the second source .of electricalpotential to bar reverse voltagelirom said transistor, and a thirddiodebackbiasedfacross the 7 load 'to bar any inductivezsurgefof the load .from the series combined load "and other source alternatively .to

the first'andfseccnd terminalsofthe capacitive means "so as-to eife'ctia flow of current to and said load 1 in electrical circuits including said two terminals of the series combinedload and other source.

2. A function generator COIIIpT-lSlIlg two capacitoi's -serially connected,- a first source 'of electrical potential applied at one fendof the series connect'edcapacitors, a second source ofelectricalpotential applied-atthejother "end of the series connectedcapacitors, a third source of transistors'upon therNPN transistor beginningconductionr simultaneously with V conduction. a

e serially connected,, a first source cfgelectrical "potential the PNP transistor beginning non- 5, A function generatorz ".ciomprisir'igt tw'o.capacitors applied at Oneend of thei'series' connected capacitors,

a difierent-electrical potential, tanelectrical,reference potential connected to the firstQsecohd and third' sourc'es of electrical potential to the junctureof the two capaci- -tors, a two terminalelectricalfloadhaving one terminal of the load attached tothe thirdsourceof ditferentelectrical potential, and a switching means for selectively connecting theiother terminal'of the load alternatively 1 v to 'one end of thes eries connected capacitors andrto the other end-"of 'the' seriesjconnected capacitors so as to V a: 7 second :source i of electricalf potential' applied" at the other end of the series connected Qcapacitors', a third source of al ditferent electrical potential, an electrical reference potential connectedtothefirst second and third sources of electrical] potential and-to the juncture of the two capacitors, a 'two terminal electrical load having one eifecta'fiow of electrical current from the load under the;

difierenceinthe potentials ofsaid firstand third sources said second and third sources, 1

3. A function generator ccomprisingtfou r adjustable and alternatively underthe difference 'in the potentials of 'sourcesjof electrical potential and where the first source of potential being always less than the third; and the third potential being a'lw'ays less than the fourthpotenitial, and'where the firstithird, and fourth potentials being 'floatingwith respect to the second potential; a first 'c-a- :pacitor connected. between the first and second' sources' ofrpote'ntial; a second capacitor connected between the second and third sources 'of potential; an electrical load havingtwo terminals 'of opposite polarity, said'electric-al load beingcconnected atone of said terminals-to the" fourth source of, electrical potentialy and a switching r means connected to the otherterminal ofsaid electrical i load for selectivelyconnect-ing' said other terminaljof the i load to thefirst-and the third source of electrical poten-'. f,' tial so as to effect a flow of current into saidone termi- VV anal of the load from'the fourth source'of greater potential and from said other terrninalof the load to the echo! tively connected source of lesser potential, V 7

4. A "function generator comprising two capacitors serially connected,ia;.first source of electrical potential V fapplied at one end of the se'ries connected capacitorg a secondsource of -electrical'potential applied at ithe other endof the; series connected-capacitors, a third i rsource-rof ajditferentQelectric'al potential, an electrical referencefpotential connected to the first, second and thirdterminal of the load attachedto-the third sourcelof different electrical potentiahanda" switching means'for se- 'lectively connectingthe other terminal of the load alternatively to one end ofthe series connected capacitors and to the othenend of the series connectedcapacitorsi said switching means includinga' diode connected forward biased from the other terminal of thefload to the I second source of electrical potential, a transistor having a 'base, an,emi-tter, and a" collector and with thecemitter and the collectorf serially connected between said other terminal of'the load and the first electrical potentialg'reversin'g means applied to the baseof said transistor 1 for selectively making said transistor conduct and nonconductfand a shunting-speed up resistorconnected in parallel with the loadgto permit any-capacitance of the conducting-to nonconducting state, 7 I V a ,7

6. A function generator comprising; tour adjustable ,load" to discharge after the tr'ansis'tor'hasgone from a 7 sources of electrical potential including the first source 10f potential being always'les's than the"third,;the third potential I being 'always less than the fourthgpotential, and the first, the third,' and the fourth potentials being k floating with respect to the second potential, -a .first-cal-pacitor connected between 'the first and second sources 'of'potential, a second capacitor connected biet fien the second 'and'third sources of p'otent-iaLa load having two 7 nected .to" said other terminal of the load' for s elective'ly switching sa'idoth'er terminal'ot theload'alte'rnatively to terminals and including, reactance elements, the load 1 "being connected {at onefof said terminals to the fourth source of electricalipotentialt'andfa switching means con- ;the first and the third source of electrical potentiiah'said switching'n eansincluding a NPN and a PNP transistor each-having a base, an emitter, an'd a collector and with the bases joined together and :ivithithef'emitters joined together; said emitters connectedfto the other: side'of the load, and withitl efccllectort in ranets connected to the third source of electrical potential, and with the collector of the PNP transistor connected to the first source of electrical potential, a reversing circuit connected between the bases and emitters of said two transistors for selectively simultaneously turning on one transistor and turning off the other, a diode forward biased between the other side of the load and the third source of electrical potential for maintaining the load in a fixed electrical potential when the NPN transistor is in a conducting state, a second diode connecting from :the col lector of the NPN transistor to the third source of electrical potential to bar reverse voltage from said transistor, and a third diode back biased across the load to bar any surge of the load from the transistors upon the NPN transistor turning on simultaneously with the PNP transistor turning off.

7. A function generator comprising two capacitors serially connected, a first source of electrical potential applied at one end of the series connected capacitors, a second source of electrical potential applied at the other end of the series connected capacitors, a third source of a different electrical potential, an electrical reference potential connected to the first, second and third sources of electrical potential and to the juncture of the two capacitors, a two terminal electrical load having one terminal of the load attached to the third source of different electrical potential, and a switching means for selectively connecting the other terminal of the load alternatively to one end of the series connected capacitors and to the other end of the series connected capacitors; said switching means including a transistor having a base, an emitter, and a collector; the collector being connected to the other terminal of the load and the emitter connected to the first source of electrical potential; a driving circuit connected between the base and emitter for selectively rendering the transistor conducting and.

nonconducting; a diode connected from the collector to the second source of electrical potential; and a speed up shunt load resistor connected from the collector to the third source of electrical potential.

8. A function generator comprising two capacitors serially connected, a first source of electrical potential applied at one end of the series connected capacitors, a second source of electrical potential applied at the other end of the series connected capacitors, a third source of a different electrical potential, an electrical reference potential connected to the first, second and third sources of electrical potential and to the juncture; of the two capacitors, a two terminal electrical load having one terminal of the load attached to the third source of different electrical potential, and a switching means for selectively connecting the other terminal of the load alternatively to one end of the series connected capacitors and to the other end of the series connected capacitors; said switching means including a transistor having a base, an emitter element and a collector element; one of said elements being connected to the other terminal of the load and the other of said elements being con nected to the first source of electrical potential; a driving circuit connected between the base of the transistor and the first source of electrical potential for selectively rendering the transistor conducting and nonconducting; a diode connected from the juncture of the other terminal of the load with the one element of the transistor to the second source of electrical potential, and a speed up shunt load resistor connected across the load.

9. A function generator comprising two capacitors serially connected; a first source of electrical potential applied at one end of the series connected capacitors; a second source of electrical potential applied at the other end of the series connected capacitors; a third source of potential; first load means, second load means, said first and second load means being attached to the third source of electrical potential; and switching means for selectively connecting the first and second load means alternatively to one end of the series connected capacitors and to the other end of the series connected capacitors, said switching means including a pair of transistors each having a base connection, an emitter terminal, and a collector terminal, one of said terminals of each of said transistors being connected to the first source of elec trical potential, and the other of said terminals of one of said transistors being connected to the first load means and the other of said terminals of the other of said transistors being connected to the second load means, a driver circuit means connected between the first source of electrical potential and the base connections of the transistors for selectively simultaneously rendering one of said transistors conducting and the other of said transistors nonconducting, and two diodes, one each of said diodes connecting a junction of the first and second load means with said transistors to the second source of electrical potential.

References Cited in the file of this patent UNITED STATES PATENTS 2,514,434 .Wl'ndes July 11, 1950 2,916,702 Bigelow Dec. 8, 1959 2,991,372 Blocher July 4, 1961 3,049,630 Sapino .Q Aug. 14, 1962 

1. A FUNCTION GENERATOR COMPRISING CAPACITIVE MEANS HAVING A PLURALITY OF TERMINALS; A SOURCE OF ELECTRICAL POTENTIAL CONNECTED TO THE CAPACITIVE MEANS FOR IMPRESSING A POTENTIAL AT FIRST AND SECOND TERMINALS OF THE CAPACITOR MEANS; ANOTHER SOURCE OF A DIFFERENT ELECTRICAL POTENTIAL AND AN ELECTRICAL LOAD SERIALLY COMBINED WITH SAID OTHER SOURCE AND HAVING TWO TERMINALS, ONE TERMINAL OF THE SERIES COMBINED LOAD AND OTHER SOURCE BEING CONNECTED TO A THIRD TERMINAL OF THE CAPACITY MEANS, AND MEANS TO ELECTRICALLY CONNECT THE OTHER TERMINAL OF THE SERIES COMBINED LOAD AND OTHER SOURCE ALTERNATIVELY TO THE FIRST AND SECOND TERMINALS OF THE CAPACITIVE MEANS SO AS TO EFFECT A FLOW OF CURRENT TO AND FROM SAID LOAD IN ELECTRICAL CIRCUITS INCLUDING SAID TWO TERMINALS OF THE SERIES COMBINED LOAD AND OTHER SOURCE. 